A 25-year-old soccer player injures her knee and presents with a positive anterior drawer test, positive Lachman test, and a pivot-shift test. MRI confirms an ACL tear with a bone bruise at the lateral femoral condyle and posterolateral tibial plateau. The mechanism of injury responsible for this 'kissing contusion' pattern is:
- A Direct contact blow to the medial aspect of the knee causing valgus stress
- B Hyperextension injury of the knee causing posterior capsule tear
- C Twisting fall causing isolated medial meniscus tear
- D Non-contact deceleration or rotational mechanism with the knee near extension — causing anterior tibial subluxation where the posterolateral tibial plateau impinges against the lateral femoral condyle ✓
Explanation
The bone bruise pattern of lateral femoral condyle (anterior aspect) and posterolateral tibial plateau on MRI is pathognomonic of ACL tear from a non-contact pivot/deceleration mechanism. When the ACL ruptures, the lateral tibial plateau subluxates anteriorly beneath the lateral femoral condyle (the pivot-shift mechanism); this impaction creates characteristic trabecular microfractures (bone bruises) at the two contact points. This pattern is highly specific for ACL disruption and is important to identify as it suggests a rotational mechanism and higher energy injury. Direct medial valgus contact causes MCL injury with medial bruising, not this lateral pattern.
Reference: Maheshwari Essential Orthopaedics, 6th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.